Amplifiers are commonly used in electronic equipment in order to amplify device characteristics, such as gain, bandwidth and linearity. Amplifiers are widely used in active filters, buffers, analog-to-digital converters, and radio frequency (RF) transceivers. In wireless communication applications, power amplifiers, as an essential part in RF circuits, are normally disposed at the front end of an antenna transceiver. The main function of a power amplifier is to enlarge output signals, and is the most power-consuming part in the RF front-end circuit.
A biasing circuit is usually used for supplying bias current or bias voltage to a power amplifier, so that the power amplifier may operate in a linear region for amplifying signals. The biasing circuit includes a main bias block and a gain-correction block. The main bias block is configured to generate bias current. The gain-correction block is configured to generate correction current for adjusting the value of the bias current, thereby compensating gain variations as the power amplifier switches from a disabled state to an enabled state. For example, when the power amplifier is just activated, it remains to operate in a transient state due to temperature effect for a period of time before being able to operate in a stable state. Since the gain in the transient state is lower than the gain in the stable state effect, the gain-correction block can provide the correction current at initial activation of the power amplifier so as to compensate the smaller gain in the transient state. However, the prior art biasing circuit usually provides the correction current using current mirrors which consume a lot of power. Therefore, there is a need for a boost circuit capable of shortening transient response for use in a power amplifier while minimizing the use of current mirrors.